Telephonic trunk-circuit



Patenten Apr..2.5, |899.

T. c. wALEs, 1n. 3. H.M.;CBANE.'

no.' azz-1,533.4

TELEPHoNlc Tnumcclcun.

(Application led Sept. 29,1898.)

(No Mpdel.)

Nonms PETERS co.. PNoTaLn'r-m llrrn T'Arns THOMAS C. WALES, JR., OFNEWTON, AND HENRY MIDDLEBROOK CRANE,

OF BOSTON, MASSACHUSETTS, ASSIGNORS TO THE AMERICAN BELL TELE- PHONECOMPANY, OF BOSTON, MASSACHUSETTS.

TELEPHONIC TRUNK-CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 623,583, dated April25, 1899.

Application iiled September 29, 1898. Serial No. 692,240. (No model.)

To all whom t may concern,.-

Be it known' that we, THoMAs C. WALES, Jr., residing at Newton, in-thecounty of Middlesex, and HENRY MIDDLEBROOK CRANE, re-

siding at Boston, in the county of Suffolk, State of Massachusetts, haveinvented certain Improvements in Telephonie Trunk-Circuits, of which thefollowing is a specification.

This invention relates to trunk circuits io by means of which distanttelephone substation-circuits which terminate at independentswitchboards are connected with one another.

The trunk circuit herein referred to is adapted for the interconnectionof that type of substation-lines known inthe art as relaycircuits, inwhich a centralized source of current is employed by the substation bothfor signaling the central station and for energizingtelephone-transmitters.

The present trunk-circuit is adapted for use in either direction-t'. e.,it is symmetrical in arrangement and reversible or reciprocal inoperation-and is therefore provided at each end with multiple switchconnections and means actuated by the operation of any of the saidswitch connections for establishing a determinate electrical conditionat the remaining switch connections at each end, and With means at eachswitch connection for testing 3o the said electrical conditiontoascertain at any switch connection at either end whether thetrunk-circuit is or is not already in use.

The invention also relates to the associated automatic signals wherebythe operators are instructed as to the condition and requirements of thecircuit and its operation. To carry out the full operation of theinvention, it is necessary to provide different forms of connectingcord-circuits at each trunk-terminal, one of which will be used by the Aor calling operator in initiating a connection and the other to be usedby the B or receiving operator in responding to a call.A

In the drawings which accompany the speciication, Figure lis a diagramillustrating the application of the invention and showing thetrunkcircuit thereof in association with two substation-circuitsconnecting with two switchboards, and Fi 2 is a diagram illustrative ofthe said trunk and substation circuits connected up as aconversation-circuit.

As the general arrangement of the relayswitchboard substation-circuitsis now well known in the art, no extended description is necessary. y

A and B are two substation-circuits extending from ltheir respectivesubstations X Y to two independent switchboards, (designated as D andvF,) and E is the trunk-circuit extending between the said switchboards.The said substation-circuits have terminal jacks or switch-sockets ontheir respective switchboards; but the line or call-signal appliancesAot the circuitA only are shown. E is the said trunk-circuit, consistingof the conductors 'm4 and w, extending from the armatures fand. f of therelay C2 to the armatures f2 and f3 of the similar relay C at theopposite end. Normally each upper armature f2 is connected through itsback contact and a relay L2 L to ground, and lower armature f isconnected through a resistance r2 with the test-rings of the lin e-jacksJ J, and also through resistance R2 and a signal S to ground, whilearmature f3 is connected through a resist-ance r with the test-rings ofline-jacks J 3 J 5,' and also through resistance R and a signal S2 toground. The test-rings J J are also connected with the cutoff relay C2and to ground. The armature of the line-relay Lz'is, with a battery B2,in a ground branch and adapted to light the sig- 'nal S when attracted.The test-rings J 3 J 5 are also similarly connected with a cut-off relayC and to ground, and the armature of the line-relay L is, with a batteryB5, in a ground branch and adapted to light the signal S2 whenattracted.

The cord-circuit shown at central station D and termed herein theanswering-circuit is a standard circuit used with switchboards of thistype and is arranged differently from the cord-circuit shown at thecentral station F and designated as the connecting cordcircuit, and thenecessity therefor will be apparent. Consequently to insure that thecircuit will be reversible or reciprocal'the A operators at both centralstations are provided with cord-circuits, as shown at the central teryB', an induction-coil divided into four windings, two ot which connectone pole of the battery with the tips of the plugs, while the other twoconnect the plug-sleeves and include in each side shul'iting-relays RR3, respectively, and the test-ring plug-sleeves are connected with eachother and are provided with disconnect-signals S and S'and a groundbranch including a battery B. Each signal is adapted to be shunted bythe armature of the said relays. In the cord-circuitat F thesleeve-conductor of the plug P3 is connected to the upper right-handwinding of the ind notion-coil and includes condenser e, which isadapted to be shunted by the armature f3 ot' relay R4 in thesleeve-conductor of the plug P4. The tip of plug P3 is connected withthe lower right-hand winding of said coil, and the signal Sl in thetest-ring-sleeve conductor w3 ot' the plug P3 is arranged to be shuntedby the relay R3 in the tip-conductor of said plug.

In the operation of the invention suppose that a subscriber at X wishesto be put in connection with asubscriber at Y. When the telephone at Xis removed from its support, the line-signal S3 is lighted, and inresponse to this the receiving operator, termed the A operator, insertsthe plugPof aconnecting or looping cord-circuit into a jack J,associated with the line of the calling substation, and ascertainingthat substation Y is wanted touches the tip of the second plug P to thering of a jack J' of the selected trunkeircuit to ascertain whether itis already in use or not. Finding the circuit idle, the plug P' isinserted into jack J'. The effect of this is to place a busy test uponthe trunkcircuit and to operate the cut-oFf relay C2. This isaccomplished by a flow of current from battery B through signal S andrear sleeve of plug P' of the answering and connecting cord-circuit,ring of jack J', conductors u: and w3, and cut-off relay C2 to ground.The cut-off relay C3 byits operation opens the tru uli-circuit byattracting the armatures fand f', and the test-rings of all the jacksconnected with the trunlccircuit at office D are raised to a potentialabove that of the earth. As a result of this the usual busy test will beobtained should any operator at station D touch her plug to anytest-ring of the circuit. In addition to the operations described by theinsertion of a plug P into jack J' current also flows from battery B',relay R, and front sleeve of plug P' of the cord-circuit, spring yw3 ofthe jack, conductor 104, armature f3 of cut-olf relay C and line-relay Lat the second central station F. This current causes relay I.' toattract its armature and close the local circuit of signal-lamp S3,which is placed before the connecting or B operator. Vhen the armatureof relay Il' is attracted to its rent ows from the battery B5 throughresistance R' to the wire w3 and to the testrings of the jacks J3 and J5, which are thus raised to a potential above that of the earth and whena test is made with a calling-plug the usual click will be heard in theoperators telephone. Thus the trunk-circuit is made to test busy at allof the jacks at both of its terminals. In response to the operation ofthe signal S2 the operator at station F inserts plug P3 of theconnecting cord-circuit into jack J3 and learns from the A operator atstation D the number of the called-for circuit. The insertion of thisplug permits current to flow from battery B3 through signal S3,conductor w3, and rear sleeve of plug P3 of said cord-circuit, ring ofjack J3, conductor 107, and cut-off relay C to ground. This currentoperates relay C, causing it to attract its armatures f2f3 to open themain conductors wt and w3 and to cut ott the current from battery B atthe station D, whereupon the armature of line-relay L' returns to itsnormal posit-ion and the signal-lamp S2 is extinguished. Then thecircuit is broken at f4, the busy test already described is removed fromthe rings of the jacks at the station F as the battery B5 is cut off;but current from battery B3 Hows, as described, to the said rings, andtherefore there is no interruption of the busy test during the transferfrom battery B2 to battery B3. In fact these batteries may-be identical.This flow of current from the battery B3 would cause the B oper.- atorsdisconnect-sign al S4 to operate were the signal not short-circuited bythe armature of the cord-circuit relay R3, which is drawn up by thelowot' current from battery B1 through relay R3, tip of plug P3, lowerspring w3 ot' roo jack J3, conductor w3, spring w10 of jack J at stationD, tip of plug P', and coil-winding K to ground. By operating the usualkey the B operator is enabled to place the listeningtelephone Z acrossthe trunk-line circuit and to receive the number of the desiredsubstation-line, whereupon she inserts plug P4 into jack J4 of this lineand rings the bell at the substation in the usual manner. The subscriberat Y in answering removes the telephone from its hook-switch and bridgesthe transmitter T and the helices s and j? of the induction-coil Iacross the line in series with the telephone. In this way a path ofrelatively low resistance is offered to the current which ows frombattery B4, relay R', ring or front sleeve ot plug P4, upper spring ofjack J4, through the substation-line andset, returning through lowerspring of jack J4, tip of plug P4, and through the operator-'scord-circuit induction-coil to the battery. This current operates relayR4, which attracts its armature, thereby short-circuiting condenser fu.The etect of this is to allow current to How from battery B' at stationD through coil-winding K3, cord-circuit relay R, ring of plug P', upperspring w3 of jack J',

front contact and the signal S2 is lighted, eurconductor to', upperspring w10 of jack J3,

IIO

ring-sleeve of plug P3, conductor w11, armature f of relay R4, conductorw12, and coilwinding K5 to ground. relay R at station D to operate,thereby shortcircuiting signal S, which up to this time has displayedits shutter, owing tothe ow of current from battery B through sleeve ofplug P', ring of jack J', conductors w and 102, and cut-off relay C2 toground. If the present state of the main circuit'is examined, it will beseen that so far as transmission is concerned the substations X and Yare connected by the simple circuit shown in Fig. 2. Vith regard tosignaling it is evident that signal S in the A operators cord-circuit atstation D is controlled by the switch-hook at substation X. Signal S ofthe said cord-circuit is immediately controlled by the relay R, whichoperates to short-circuit it, and relay R is in turn controlled by relayR4 in the B operators cord-circuit at station F, as has been previouslydescribed. Furthermore, relay R4 is directly controlled by thehookswitch at substation Y, and thus the signal S is indirectlycontrolled by said substation. The arrangement for signaling brings theentire supervision of the connection under the.

care of the A operator at station D, where it should be. Upon thecompletion of conversation the telephones at the substations arereplaced upon their hooks and the signals S' and S are respectivelyoperated, thus informing the operator at station D of the termination-ofthe conversation, upon which she withdraws plug P/ from jack J. Thisoperation interrupts the flow of current through cutoff relay C2, whosearmatures then return to their normal position upon their back contacts.The Withdrawal of the plug also causes a cessation of current, which upto this time has been lowing from battery B4 through relay RS, ashereinbefore mentioned, which short-circuits the signal S4, and when thearmature of said relay'falls away the current' from battery B3 causesthe signal to be lighted.

The busy test already described for the trunk-circuit at the station Ddepends upon the plug P being in the jack J, and afterthe withdrawal ofthe plug the test is continued as follows: Vhen the plug is withdrawnand the armatures f and f2 close upon their rear contacts, as stated,there exists a connection from battery B4 at station F through relay R3,tip of plug P3, spring w8 of jack J3, conductor w, armature f of relayC2 at station D, resistance r2, conductor w14 and w to the test-rings ofall the jacks of this trunk-circuit at station D, thence throughresistance R2, signal S to ground, and this busytest will remain uponall the test-rings at both stations D until the B operator at the latterstation withdraws plug P3 from jack J3, which operation will restore theentire circuit to its normal position. As herein stated, theseoperations are reversible-fi.. e., the call for a connection can beinitiated from the central station F and the several operations be per-This current causes rocal operation, and provided with multiple switchconnections at each switchboard; means actuated by the operation of anyof the said switch connections at either switchboard for establishing adeterminate electrical condition at the remaining switch connections ofboth switchboards; and means at each switch connection of bothswitchboards for testing the said electrical condition whereby it may beascertained at any switch connection of the said trunk-circuit at eitherswitchboard, whether the said trunk is or is not already employed at anyother switch connection of the said two switchboards; substantiallyasset forth.

2. The combination substantially as hereinbefore described, of areciprocally-operated in terswitchboard telephon e trunk-circuitprovided with multiple switch connections upon the switchboards at bothof its ends; with a Abusy-test system adapted to establish a special andabnormal electrical condition as long I OO as the said trunk is switchedat any one of its multiple connections,at either end thereof, in andupon the switch-sockets at all of the remaining switch connections ofboth switchboards.

Inatelephone-exchange system,the combination of the herein-describedreoiprocallyoperated tru nk-circuit extending between two independentswitchboards; two subscribers circuits extending to the saidswitchboards respectively from different substations,where theirelectrical condition is cont-rolled by a switch; a connectingswitchboard-circuit at each switchboard uniting the saidsubstationcircuits with the two ends of the said trunk respectively; acondenser in one branch of the switch-cord at one of the switchboards,and a shunt-circuit therefor; a relay in the other branch of the saidswitch-cord responsive to the operation of the substation-switch andcontrolling the continuity of the said shunt-circuit; and a signal inthe cord-circuit at the other switchboard responsive to the shunting orunshunting of the said condenser; substantially as and for the purposesspecifled.

In testimony whereof. we have signed our names to this specification, inthe presence of two subscribing witnesses, this 12th day of September,1,898.

THOMAS C. WALES, Jn. HENRY MIDDLEBROOK CRANE.

Witnesses GEO. WILLIS Pinnen, JOSEPH A. GATELY.

IIO

